The detection and quantification of small quantities of Cr in (La,Sr)MnO3/Y–ZrO2 solid oxide fuel cell (SOFC) cathodes by energy-dispersive X-ray spectroscopy (EDXS) is not straightforward as Cr X-ray emission lines overlap with La/Mn and O lines. This work proposes an empirical law correlating the La peak height ratio Lb2.15/La1 to Cr concentrations determined on Cr-doped LSM–YSZ samples characterized by EDXS. Calibration for the law was obtained by chemical analysis of dissolved cathodes. Quantification was confirmed by wavelength-dispersive X-ray spectroscopy.